The fundamental renal (kidney) filtration unit, which removes harmful waste products from the blood and produces urine, is a complex anatomical structure called a nephron. Human kidneys serve to convert in excess of 1700 liters of blood per day into about 1 liter of urine; each human kidney contains approximately one million nephrons. Each nephron is comprised of a vascular component and a tubular component. The glomerulus, the principal vascular component, is a convoluted semipermeable capillary network through which part of the water and solutes are filtered from the blood passing through. The glomerular basement membrane acts like a sieve to retain cells and large protein molecules, while passing water and soluble wastes. The filtered fluid (also called nephritic filtrate), which is almost identical in composition to plasma, then enters the tubular portion of the nephron. The tubular portion is comprised of a sequential series of ducts, including a proximal tubule, a loop of Henle, a distal tubule, and a collecting tubule, which lead to a ureter and thence to the urinary bladder. Much of the water, salts, and nutrients initially passed by the glomerulus are reclaimed by the nephron via various transport processes before the filtrate completes its transit to the bladder.
Renal dysfunction, or when associated with a disease, renal disease (disease of the kidneys) can have many causes, including but not limited to: drugs, toxic substances, antibiotics, infections, diabetes, and cancer. The kidney is a highly complex structure of primarily four systems (including vascular, glomerular, tubular, and interstitial regions), and the anatomical interdependence of these structures implies that damage to one structure usually affects the others secondarily. Thus, there is a tendency for all forms of chronic renal damage to eventually destroy all four systems. In addition, because the kidneys have a large functional reserve, much damage may occur before clinical symptoms are manifest. Thus, kidney disease is commonly insidious, and detection of early signs and symptoms is especially important.
Multiple myeloma, a malignant tumor of plasma cells, is commonly associated with osteolytic lesions (lytic bone loss), recurrent bacterial infections, anemia, and chronic interstitial nephritis (inflammation of the interstitial tissue of the kidney) leading to renal failure. The etiology of multiple myeloma (also called myeloma) is unknown, but the frequency of this disease in patients with monoclonal gammopathy of undetermined significance (marked by the presence in serum of monoclonal immunoglobulins IgA or IgG) is high. Moreover, the presence in families of both multiple myeloma and monoclonal gammopathy of undetermined significance suggests a genetic link between these diseases.
The American Cancer Society estimates that more than 15,000 new cases of multiple myeloma will be diagnosed in 2004, and that more than 11,000 Americans will die of multiple myeloma in 2004. American Cancer Society, Cancer Facts & Figures 2004.
In multiple myeloma, the source of renal involvement is overproduction of antibody light chains (Bence-Jones proteins), which aggregate in the distal convoluted tubules and collecting ducts of the kidneys, forming proteinaceous casts. Antibodies are produced by immune cells called plasma cells, which arise from activated B lymphocytes (B cells). Each B cell produces a unique receptor (B cell receptor), specific for a foreign substance and arrayed on the cell surface. When a B cell receptor recognizes its cognate antigen (foreign substance), the cell carrying that receptor becomes activated, re-enters the cell cycle, and produces many clonal copies of itself. These clones mature into plasma cells, which reside principally in the bone marrow. Plasma cells are specialized to produce copies of the B cell receptor, which are then released to the bloodstream as antibodies (immunoglobulins). Immunoglobulins are comprised of four protein chains: two long chains called heavy chains, and two shorter chains called light chains.
In multiple myeloma, the mother B cell suffers genetic damage resulting in suppression of or insensitivity to the normal restraints on cell division. Thus, the daughter plasma cells produced by such a B cell are malignant—they continue to divide unchecked, creating more malignant plasma cells, and generating multiple copies of the same immunoglobulin (also called monoclonal protein, M protein, or paraprotein) in excess amounts. An elevated level of M protein in the blood is a hallmark of multiple myeloma, but up to 20% of patients with myeloma produce only the light chain portion of the immunoglobulins, called Bence-Jones proteins (a subset of the “M protein” group). In such patients, these free monoclonal light chains are found principally in the urine instead of the blood, having passed through the renal filtration mechanisms. Bence-Jones proteins may precipitate from solution while passing through the distal convoluted tubules and collecting ducts of the kidney, forming proteinaceous deposits (also called “casts”) therein. These casts clog the renal tubular network, cause damage to surrounding epithelium, and initiate inflammatory cascades, leading eventually to renal failure. Hypercalcemia, hypercalciuria, and hyperuricemia may also contribute further damage. “Myeloma kidney” is characterized histologically by interstitial fibrosis and hyaline casts surrounded by epithelial cells or multinucleate giant cells.
Pituitary adenylate cyclase activating polypeptide (PACAP) was originally isolated from ovine (sheep) hypothalamic tissues based on its ability to activate adenylate cyclase in rat pituitary cell cultures. Miyata et al. Biochem Biophys Res Commun. 164: 567 (1989). PACAP is a neurotransmitter and neuroendocrine hormone, and exists in two active forms: a long form, with 38 amino acids (PACAP38), and a C-terminally truncated form with 27 amino acids (PACAP27). Miyata et al. Biochem Biophys Res Commun. 170: 643 (1990). The amino acid sequences for these two versions are shown in FIG. 1 (SEQ ID NO:1 and SEQ ID NO:2). PACAP is a member of the secretin/glucagon/vasoactive intestinal peptide family, the N-terminal region being 68% homologous to VIP (SEQ ID NO:3), yet its adenylate cyclase stimulating activity in cultured pituitary cells, neurons and astrocytes is about 1,000-10,000 times greater than VIP. Miyata et al. (1990), supra. PACAP is a pleiotropic neuropeptide, exhibiting a number of neurotrophic activities in different organs and tissues. For example, PACAP enhances proliferation and differentiation of sympathetic neuroblasts, stimulates neurite outgrowth of an adrenal chromaffin cell line (PC-12 pheochromocytoma cells), and stimulates growth of astrocytes. Arimura A. Regul Pept. 37: 285 (1992); Okazaki K, et al. FEBS Lett. 298: 49 (1992). The in vivo cytoprotective action of PACAP has been investigated in rats with transient forebrain ischemia. Uchida et al., Soc Neurosci Abst., Vol. 20, 1994 (Abstract No. 193.10).
One of the activities of PACAP is its ability to bind one or more PACAP receptors. There are at least three known PACAP receptors: PAC1-R (type I PACAP receptor); VPAC1-R (type II PACAP receptor, or type I VIP receptor); and VPAC2-R (type II VIP receptor, or VIP2). Gottschall P E, et al. Endocrinology. 127: 272 (1990); Shivers B D, et al. Endocrinology. 128: 3055 (1991); Arimura A. Trends Endocrinol Metab. 3: 288 (1992). PAC1-R, which is found in the hypothalamus, brain stem, pituitary, adrenal gland, pancreas, and testes, specifically binds to PACAP with high affinity, but does not bind to VIP. Ogi K, et al. Biochem Biophys Res Commun. 196: 1511 (1993). VPAC1-R and VPAC2-R both bind PACAP and VIP with similar high affinities. Sreedharan S P, et al. Proc Natl Acad Sci USA. 92: 2939 (1995); Svoboda M, et al. Biochem Biophys Res Commun. 205: 1617 (1994).
Standard treatments for multiple myeloma include: chemotherapy; autologous stem cell transplantation; and thalidomide. Dexamethasone (a steroid) is currently used to protect against renal damage induced by the light chains, and to suppress tumor cell proliferation. However, the side effects of long-term dexamethasone administration are of serious concern. In particular, chronic dexamethasone treatment can cause osteoporosis, thus reducing its utility in myeloma therapy because a major sequela of myeloma is bone resorption. Thus there is a need to obtain an improvement over existing therapies for multiple myeloma and renal disease.
Citation or discussion of a reference herein shall not be construed as an admission that such is prior art to the present invention.